WASHINGTON (Reuters) – Independent experts have satellite imagery of what they believe to be a Syrian nuclear site targeted in an Israeli air strike last month, The Washington Post reported on Wednesday.

The Institute for Science and International Security (ISIS) said the photographs taken before the Israeli attack show buildings under construction similar in design to a North Korean reactor, the newspaper reported.

They also show what could have been a pumping station used to supply cooling water for a reactor, the Post said, citing experts David Albright and Paul Brannan of ISIS, a research group that tracks nuclear weapons and stockpiles.

Israel, an important ally to the United States in the region, has confirmed it carried out an air strike on Syria on September 6 but has not described the target. Syria said only that the target was a building under construction.

Albright, a former U.N. weapons inspector, said the size of the structures suggested that Syria might have been building a gas-graphite reactor similar to the one North Korea built at Yongbyon, the paper reported.

According to an ISIS report to be released on Wednesday, the Euphrates River site is just north of the desert village of At Tibnah in the region of Dayr Az Zawr and about 90 miles from the Iraqi border, the Post reported.

The Washington Post said some nuclear experts urged caution in interpreting the ISIS photos, noting the type of reactor favoured by North Korea has few distinguishing characteristics visible from the air.

“You can look at North Korea’s (reactor) buildings, and they look like nothing,” John Pike, a nuclear expert and director of GlobalSecurity.org, told the Post.

The New York Times reported last week the site targeted by Israel was modelled on a facility North Korea used for stockpiling atomic bomb fuel.

Syria has one declared, small research nuclear reactor under safeguard of the International Atomic Energy Agency and has denied hiding any nuclear activity.